The present invention relates to print head motor control systems and more particularly to a print head motor control system in which the steady-state velocity is monitored and adjusted for correctness incrementally by equal amounts during predetermined time intervals.
Typically, in the past, printers have operated at a single or at best just a few different speeds. In these types of systems, normally a conventional servo-mechanism velocity control system has been employed. In such conventional systems, the steady-state velocity is adjusted to a desired value by taking the difference between the measured speed and the desired speed and changing the drive voltage of the motor by a magnitude which instantaneously attempts to correct the steady-state speed to the desired value. However, in printers where numerous different print head speeds are utilized, such a steady-state control method would be extremely difficult because of the large number of velocity references required and instability could result if sufficient processor bandwidth is not utilized for velocity compensation.
The present invention employs a technique which incrementally adjusts the measured speed by equal amounts towards the desired speed during predetermined time intervals, rather than trying to instantaneously adjust the measured speed to the desired speed, and thus provides a suitable system for multispeed printer operation requiring a minimum of micro-processor bandwidth.